Present processes for the direct oxidation of diolefins to furan compounds are primarily vapor phase processes which are generally characterized by low conversions and poor selectivities. These disadvantages are brought about by the instability of furan compounds at high temperatures in the presence of oxygen which leads to the formation of resinous compounds, charring and uncontrolled polymerization. The liquid phase process of the present invention eliminates these disadvantages by operating at moderate temperatures.
Although several liquid phase processes are known for the production of furan compounds, they involve the use of oxygenated compounds as starting materials. For example, U.S. Pat. No. 3,932,468, issued Jan. 13, 1976, and U.S. Pat. No. 3,996,248, issued Dec. 7, 1976, pertain to the rearrangement of butadiene monoxide, and U.S. Pat. No. 3,933,861, issued Jan. 20, 1976, involves the reaction of an alkene and an alkene oxide to yield substituted furans. Both of these processes require oxygenated starting materials, whereas in the present invention, furan compounds are obtained by the direct oxidation of the conjugated diolefin.
While Japanese Pat. No. 77 77,049 discloses a process for the oxidation of butadiene to furan in an aqueous acidic medium, the process of the present invention is distinguished from this process in that the present process is conducted in an organic solvent medium in which the catalyst and furan products are more stable.